My present invention relates to a double-acting mechanical metal working machine, especially a forging machine, of the type in which an eccentric serves to drive a ram. More particularly, the invention relates to a metal forming machine, especially a forging press, having a combined eccentric and toggle drive for a ram which can be subdivided into an outer ram member and an inner ram member respectively acting on outer and inner tool parts.
Forging presses utilizing eccentrics or toggle drive systems are described, for example, in DE 37 05 235 C2 and EP 0 040 965 A2. These systems, however, are generally suitable for single stage operations only. Double-acting metal working machines are, however, known but utilize generally a hydraulic pressure cushion for at least one of the tool actions. The drawback in such a system is that the magnitude of the hydraulic pressure is usually limited to the capacity of the pressure cushion and may not be able to exceed 5000 kN. In some cases, however, the press may have to overcome the hydraulic pressure and as a result there are energy and force losses in the operation of such presses. Furthermore, the press must be dimensioned to be capable of supporting excessive pressures.
Double-acting presses utilizing hydraulics have not been found to be fully effective with respect to the flow or plastic deformation of the metal, especially in the case of gear fabrication and have had disadvantages with respect to formation of burrs and the like in the forging of gears.
It is, therefore, the principal object of the present invention to provide an improved double-acting metal forming machine, especially a forging machine which is free from the drawbacks previously mentioned.
Another object of this invention is to provide an improved double-acting metal working machine which is especially suitable for the forging of gears without detrimental burrs and under more effective material-flow and plastic deformation conditions than has been possible heretofore.
It is yet another object of the invention to provide a versatile double-acting forging press which is of more economical construction and capable of more universal use for the shaping of metals than has heretofore been the case.
Yet another object of this invention is to provide an improved double-acting metal forming machine which can optionally be employed for a single acting tool or die system and which operates mechanically, i.e. without hydraulic ram actuation.
These objects and others which will become apparent hereinafter are attained, in accordance with the present invention, by providing a double-acting metal working machine, especially a forging press, having an outer ram member which can be driven by an eccentric drive and an inner drive member which is driven by a toggle drive or mechanism such that the eccentric shaft can drive the entire ram or only the outer ram member.
The toggle mechanism, which can be effective selectively to act upon an inner tool part when desired can alternatively be ineffective when the latter actuates the ram as a whole in the case in which double action upon the tool is not desired or in an initial stage when the toggle mechanism is to be subsequently effective on, for example, the inner tool part.
The double-acting system of the invention allows the eccentric drive to act upon the outer ram member and the crank mechanism on the inner ram member and hence upon the tool parts which are coupled to these ram members. In this case, the characteristics of the metal working machine can be varied as may be required since it is possible to operate without the effects of the toggle mechanism.
The press can thus operate either as a single stage eccentric press or as a two-stage or double-acting mechanical press.
Since the toggle mechanism does not play a role in the displacement of the ram as a whole, especially in the case of hot forging of a tool, this disadvantageously long contact times between the tool and the workpiece can be avoided. It may be noted that such excessive contact times in hot forming cannot be avoided if, for example, the toggle mechanism would be coupled to the outer tool part and the eccentric drive to the inner tool part. The invention is also particularly effective in cold working of metals and thus the universality of the machine of the invention is an important advantage.
The double-acting metal forming of the machine can, in particular, comprise:
a machine frame;
a ram displaceable on the frame and comprising an outer ram member and an inner ram member displaceable relative to the outer ram member;
a shaping tool mountable in the frame and having an outer tool part positioned for actuation by the outer ram member and an optional inner tool part for displacement by the inner ram member;
an eccentric drive on the frame coupled selectively with the ram or with the outer ram member for displacement of the ram with both the members or only the outer ram member to shape a workpiece in the tool; and
a toggle drive on the frame coupled with the inner ram member for displacement thereof.
Advantageously, a plurality of pressure pins are receivable in the tool and are aligned with the inner ram member and with the inner tool part for coupling displacement of the inner ram member to the inner tool part. It has been found to be advantageous for the eccentric drive to include a crankshaft mounted on the frame above the ram and a plurality of connecting rods connecting eccentrics of the shaft with the outer ram member or members on opposite sides of the inner ram member.
The toggle drive can include a lever mounted on the shaft, and a toggle linkage including a pair of articulated links pivotally connected at opposite ends to the inner ram member and to the frame, the lever being pivotally connected to one of the links.
Metal forming machines with double-acting tools can be used with advantage for hot forming, semi-hot forming or cold forming. With conventional mechanical metal forming machines or presses utilizing the kinematics of the toggle mechanism and wherein that toggle mechanism acts upon an outer ram member, the significant drawback arises that at all steps the contact between the outer ram member, over its entire contact cross section, and the workpiece is maintained for a comparatively long time under the applied pressure.
When the metal work is carried out at high temperatures, like those used for hot forming, the pressure contact duration can so heat the tool that its life expectancy is greatly reduced. In fact, overheating can destroy the tool entirely. With the apparatus of the invention, this drawback does not arise. All of the parts of the tool associated with the outer ram member have the very limited pressure contact time associated with an eccentric drive, i.e. a brief contact duration and the shortest of the contact times which can arise in an eccentrically driven press.
In the double-acting mode of operation, the toggle mechanism acts on the closed tool very rapidly and does not maintain its action during the entire press stroke. Loss of energy or work is thus minimized.
The press of the invention permits replacement of the tool (die assembly) to allow the press to be converted from a double-acting press to a conventional eccentric press, i.e. a single stage press. In that case the toggle drive is decoupled from the tool. As a consequence, the press is universal for simple single action and-for double-acting metal working processes.
According to the invention, the toggle mechanism can be decoupled from the inner ram movement by removing the pressure pins which are interposed between the inner tool part and the inner ram member. In order to convert the press from a simple eccentric operation to the two-stage operation, the pressure pins, which are preferably angularly spaced from one another by 120xc2x0, need only be dropped in place in the tool cassette so that they are arranged loosely between an inner tool part and the inner ram member. Before the outer ram member performs its working stroke upon the outer tool part, the inner ram member advances the inner tool part via the pressure pins and thereby accelerates the inner tool part into engagement with the workpiece.